The present invention pertains to gas-operated burners and, in particular, to a device for automatic reignition of the flame in the case, for some reason, said flame has been extinguished.
In gas-operated refrigerators, preferably in movable installations such as caravans or the like, a burner is connected to a gas source, in the shape of an LPG cylinder, via a security valve. When in its non-actuated state the valve is closed but it can be operated manually to its open position by actuation of a push-button or the like. Accordingly, in order to ignite the burner the valve is operated in the way described and, simultaneously, an igniter is activated for the ignition of the gas streaming out. The push-button is kept pressed until the burner has been lit and the gas has been burning for a short while, in order for heating of a termocouple, positioned adjacent to the burner, to take place and the EMF of said termocouple to increase to the magnitude required for a solenoid, being part of the said valve, to be magnetized to keep the valve open even after the push-button has been released.
In movable installations, in particular, it can happen that the burner flame is blown out causing gas to escape which in unfortunate cases may lead to poisoning of people and animals or to explosions. In such a case the security valve described is activated to stop the gas supply after a short time period which may not exceed 30 seconds. Then, the amount of gas that escapes will not attain dangerous proportions.
Of course, it is a good thing that the security valve is activated when the gas flame has been blown out so that the gas supply be cut off before anything serious has happened. However, if the refrigerator is not supervised the goods stored in the refrigerator are heated gradually and may be destroyed, which is a drawback. Accordingly, devices have been proposed which sense the fact that the flame has been blown out and activates an igniter causing the flame to be reignited. It is important that the igniter be activated as soon as possible after the blowing out of the flame and in any case sufficiently before the lapse of 30 seconds when the security valve causes the gas supply to be cut oil. The EMF of the thermocouple can supply energy sufficient for the security valve to be kept open but the energy is not sufficient for moving the movable valve element of the security valve to its open position and this displacement has to take place by means of the push-button referred to above.
A known device for sensing of a flame being extinguished is based on the establishment of an electric current path between two electrodes disposed in said flame. The current is made possible by carbon particles from the gas appearing in the flame. Such a device is often referred to as ionization detector which gives a warning of extinguished flame by the fact that the absence of the flame breaks the current in the detector. This type of detector, however, has shown to give false indication in certain cases indicating the flame to be burning when in fact the flame has been blown out. This may lead to the same devastating consequences as in the case no security valve has been provided, as described above. The detector is sensitive to deposits and moisture which, under certain conditions, may give false indication. Due to the fact that a caravan is provided with a ventilation duct leading from the space surrounding the burner of the refrigerator and opening in a ventilating grill positioned on the outer wall of the caravan, cleaning agents used during wash of the caravan may enter and form a deposit on the electrodes of the detector which, in a humid environment, may cause creepage currents which cause the false indication referred to.